The purpose of the proposed studies is to elucidate, in rats, relationships between narrowly localized intracranial self-stimulation "reward" sites and the sites-of-action of high-abuse drugs such as morphine. Specifically, the proposed experiments will determine if access to rewarding brain stimulation can alleviate morphine-withdrawal symptoms in rats. They will also determine if morphine can effectively and selectively alter the sensitivity of various hypothalamus and tegmental self-stimulation sites. Finally, they will determine if fine distinctions can be made within "apparently homogeneous" self-stimulation regions with respect to morphine sensitivity.